Fix handling of snaplen field in pktHdr for packets smaller than snaplen

fako1024 · May 6, 2024 · e9e9703 · e9e9703
1 parent 556f20f
commit e9e9703
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Showing 3 changed files with 20 additions and 9 deletions.
diff --git a/capture/afpacket/afring/afring.go b/capture/afpacket/afring/afring.go
@@ -121,7 +121,7 @@ func NewSourceFromLink(link *link.Link, options ...Option) (*Source, error) {
 // NextIPPacket() methods (the latter two by calling .Payload() / .IPLayer() on the created buffer). It ensures
 // that a valid packet of appropriate structure / length is created
 func (s *Source) NewPacket() capture.Packet {
-	p := make(capture.Packet, 6+s.snapLen)
+	p := make(capture.Packet, capture.PacketHdrOffset+s.snapLen)
 	return p
 }
 

diff --git a/capture/afpacket/afring/afring_mock.go b/capture/afpacket/afring/afring_mock.go
@@ -141,7 +141,7 @@ func (m *MockSource) addPacket(payload []byte, totalLen uint32, pktType, ipLayer
 	block := m.ringBuffer.ring[thisBlock*m.blockSize : thisBlock*m.blockSize+m.blockSize]
 
 	*(*tPacketHeaderV3Mock)(unsafe.Pointer(&block[m.curBlockPos+12])) = tPacketHeaderV3Mock{
-		snaplen: min(uint32(m.snapLen), totalLen), // The snaplen is set to the totalLen if a packet is shorter
+		snaplen: min(uint32(m.snapLen), uint32(len(payload))), // The snaplen is set to the totalLen if a packet is shorter
 		pktLen:  totalLen,
 		pktMac:  mac,
 		pktNet:  mac + uint16(m.ipLayerOffset),

diff --git a/capture/capture.go b/capture/capture.go
@@ -22,10 +22,13 @@ import (
 	"golang.org/x/net/ipv6"
 )
 
-var (
+const (
 
 	// PacketHdrOffset denotes the header offset / length for storing information about the packet
 	PacketHdrOffset = 6
+)
+
+var (
 
 	// ErrCaptureStopped denotes that the capture was stopped
 	ErrCaptureStopped = errors.New("capture was stopped")
@@ -85,8 +88,12 @@ func (i IPLayer) String() (res string) {
 	if ipLayerType == 4 {
 		protocol := i[9]
 		if protocol == 6 || protocol == 17 {
-			dport = binary.BigEndian.Uint16(i[ipv4.HeaderLen+2 : ipv4.HeaderLen+4])
-			sport = binary.BigEndian.Uint16(i[ipv4.HeaderLen : ipv4.HeaderLen+2])
+			if len(i) >= ipv4.HeaderLen+4 {
+				dport = binary.BigEndian.Uint16(i[ipv4.HeaderLen+2 : ipv4.HeaderLen+4])
+			}
+			if len(i) >= ipv4.HeaderLen+2 {
+				sport = binary.BigEndian.Uint16(i[ipv4.HeaderLen : ipv4.HeaderLen+2])
+			}
 		}
 		return fmt.Sprintf("%s:%d => %s:%d (proto: %d)",
 			net.IP(i[12:16]).String(),
@@ -98,8 +105,12 @@ func (i IPLayer) String() (res string) {
 	} else if ipLayerType == 6 {
 		protocol := i[6]
 		if protocol == 6 || protocol == 17 {
-			dport = binary.BigEndian.Uint16(i[ipv6.HeaderLen+2 : ipv6.HeaderLen+4])
-			sport = binary.BigEndian.Uint16(i[ipv6.HeaderLen : ipv6.HeaderLen+2])
+			if len(i) >= ipv6.HeaderLen+4 {
+				dport = binary.BigEndian.Uint16(i[ipv6.HeaderLen+2 : ipv6.HeaderLen+4])
+			}
+			if len(i) >= ipv6.HeaderLen+2 {
+				sport = binary.BigEndian.Uint16(i[ipv6.HeaderLen : ipv6.HeaderLen+2])
+			}
 		}
 		return fmt.Sprintf("%s:%d => %s:%d (proto: %d)",
 			net.IP(i[8:24]).String(),
@@ -188,9 +199,9 @@ func NewIPPacket(buf Packet, payload []byte, pktType PacketType, totalLen int, i
 	buf[0] = pktType
 	buf[1] = ipLayerOffset
 	*(*uint32)(unsafe.Pointer(&buf[2])) = uint32(totalLen) // #nosec G103
-	copy(buf[PacketHdrOffset:], payload)
+	n := copy(buf[PacketHdrOffset:], payload)
 
-	return buf
+	return buf[:PacketHdrOffset+n]
 }
 
 // TotalLen returnsthe total packet length, including all headers